Field of the Invention
The invention relates to a permanent magnet rotor.
Description of the Related Art
As shown in FIG. 1, a typical permanent magnet rotor includes a rotor core A1 and permanent magnets A2. The rotor core A1 includes a plurality of magnetic induction blocks A11, and a plurality of radial recesses A12 are formed between every two adjacent magnetic induction blocks A11 for mounting the permanent magnets A2. The magnetic induction blocks A11 at both sides of an opening of the radial recesses protrudes to form hook blocks A13. The permanent magnets A2 are blocks including a north pole magnetic surface and a south pole magnetic surface. Two north pole magnetic surfaces of two adjacent permanent magnets A2 are separately attached to two sides of a same magnetic induction block A11 to form a north magnetic pole 100, and two south pole magnetic surfaces of two adjacent permanent magnets A2 are separately attached to two sides of another same magnetic induction block A11 to form a south magnetic pole 200.
However, in the process of magnetic domain orientation of a magnetic shoe blank, as shown in FIG. 2, when the orientation coil approaches to the permanent magnet A2, the magnetic strength of the magnetic surface close to the orientation coil is relatively strong, and the magnetic strength of the magnetic surface far from the orientation coil is relatively weak. Measurement shows that, the magnetic strength of the strong magnetic surface is at least 5% greater than the magnetic strength of the weak magnetic surface. With regard to an embedded rotor, each magnetic pole of the rotor is formed by two permanent magnets A2 separately attached to two sides of one magnetic induction block A11. If the two magnetic surfaces attached to two sides of the magnetic induction block A11 are both strong or both weak, the resulting magnetic strength is nonuniform.
In production, the nonuniformity of magnetic strength is often ignored, that is to say, the magnetic strength of the north pole magnetic surface and the south pole magnetic surface are regarded to be equivalent. However, the assembled rotor produces violent fluctuation and vibration, thereby producing irregular back electromotive force waveform, and resulting in inaccurate and inefficient control.
FIG. 3 shows two kinds of magnetic poles formed by a first strong magnetic surface and a second strong magnetic surface of permanent magnets, and by a first weak magnetic surface and a second weak magnetic surface of permanent magnets, respectively. FIG. 4 shows three kinds of magnetic poles formed by two strong magnetic surfaces, two weak magnetic surfaces, and a strong magnetic surface and a weak magnetic surface, respectively. The magnetic fields formed in FIGS. 3 and 4 are nonuniform, which is harmful to the operation of the motor. Specifically, the motor produces huge electromagnetic noise and vibration, thereby indirectly causing inaccurate and inefficient control.